Vehicle braking deployment logic for pedestrian protection leg stiffener

ABSTRACT

A method and apparatus for controlling a deployable pedestrian protection leg stiffener of a motor vehicle based upon the vehicle braking status and longitudinal acceleration.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/179,695, filed Feb. 13, 2014, and issued as U.S. Pat. No. 9,102,290,the disclosure of which is incorporated in its entirety by referenceherein.

TECHNICAL FIELD

The present invention relates generally to a deployable pedestrianprotection stiffener for a motor vehicle, and more specifically todeployment logic that considers vehicle braking, longitudinalacceleration, speed.

BACKGROUND

Most current motor vehicles include a front bumper system intended toresist and/or absorb impact loads in the event of a collision.Typically, the bumper system includes a rigid bumper beam extendingtransversely relative to the vehicle and having sufficient strength toresist a required level of impact energy. The bumper beam is mounted toand supported by the vehicle frame, sub-frame, and/or body structure. Insome cases, the bumper beam is mounted to the forward ends of a pair offrame rails which extend longitudinally relative to the vehicle and arespaced apart transversely. Often, the forward-most portion of theforward frame, immediately behind the bumper beam, comprises crush canswhich are engineered to deform or collapse longitudinally in a manner toabsorb impact energy in a predictable manner. The bumper system may alsoinclude numerous other bumper members and/or trim members connected tothe bumper beam and/or the forward frame members. Bumper systems mayalso include one or more fascia components exposed over and covering thebumper.

Several current national and multi-national vehicle safety regulatorybodies have formulated pedestrian safety standards which new vehicleswill be measured against. At least one such pedestrian safety testattempts to measure or estimate the degree of injury that will beinflicted on the lower leg of standing or walking pedestrian if struckby a relatively slow-moving vehicle. These tests generally indicate thata greater vertical distance between the bumper and the road surface mayresult in greater injury to the pedestrian's lower leg, because thelower leg may slide underneath the bumper.

Simply lowering the height of the bumper in order to improve performancein such a test may not be a practical solution because of the resultingreduction in vehicle ground clearance. Having a relatively large groundclearance is particularly important for vehicles that must operate offof paved surfaces.

It is known to provide a so-called lower leg stiffener below the bumperwhich is intended to prevent the bumper from over-riding thepedestrian's lower leg, and therefore reduce the likelihood and/or theseverity of injury during a pedestrian impact. If the stiffener is fixedit may be damaged if it strikes an obstacle in the vehicle's path.

SUMMARY

In a disclosed embodiment of a method for controlling operation of adeployable pedestrian protection stiffener of a motor vehicle, thestiffener is retracted from a deployed position if a vehicle brake isapplied and a longitudinal acceleration of the vehicle simultaneouslyexceeds a limit acceleration.

In a further disclosed embodiment of the method, the stiffener isretracted from the deployed position if a measured steering angle of thevehicle exceeds a limit angle.

In a further disclosed embodiment of the method, the stiffener isretracted from the deployed position if a measured speed of the vehicledrops below a lower limit.

In a further disclosed embodiment of the method, the stiffener isretracted only if the measured speed of the vehicle drops below thelower limit for longer than a predetermined length of time.

In a further disclosed embodiment of the method, the stiffener has aretracted position rearward of a forward surface of a vehicle bumperbeam and above a ground clearance plane of the vehicle, and in thedeployed position the stiffener is forward of the retracted position andbelow the ground clearance plane.

In a further disclosed embodiment of the method, a method forcontrolling a deployable pedestrian protection stiffener of a motorvehicle comprises deploying the stiffener if a vehicle speed exceeds afirst value. The stiffener is subsequently retracted from the deployedposition if any of the following conditions occur: 1) The vehicle speeddrops below a second value; 2) A vehicle brake is applied; and 3) alongitudinal vehicle acceleration simultaneously exceeds a limitacceleration.

In a further disclosed embodiment of the method, the first value isequal to the second value.

In a further disclosed embodiment of the method, the stiffener is alsoretracted if the vehicle speed rises above a third value greater thanthe first value.

In another disclosed embodiment, pedestrian protection leg stiffenerapparatus comprises a pedestrian leg stiffener movably mounted to amotor vehicle, an actuator moving the stiffener between a retractedposition and a deployed position; and a controller directing theactuator. The controller receives an input from a braking system of thevehicle and an accelerometer and directs the actuator to position thestiffener in the retracted position if the braking system inputindicates that a vehicle brake is applied and the accelerometer inputsimultaneously indicates that the vehicle is experiencing a longitudinalacceleration above a limit acceleration.

In a further disclosed embodiment of the apparatus, the controllerfurther receives inputs from a steering system of the vehicle anddirects the actuator to position the stiffener in the retracted positionif the steering system input indicates a steering angle exceeding alimit angle.

In a further disclosed embodiment of the apparatus, the controllerfurther receives an input from a vehicle speed sensor and directs theactuator to position the stiffener in the retracted position if thespeed sensor input indicates that a vehicle speed is below a lowerlimit.

In a further disclosed embodiment of the apparatus, the controllerdirects the actuator to position the stiffener in the retracted positiononly if the vehicle speed is below the lower limit for longer than apredetermined length of time.

In a further disclosed embodiment of the apparatus, the controllerfurther receives an input from a vehicle speed sensor and directs theactuator to position the stiffener in the deployed position if the speedsensor input indicates that a vehicle speed exceeds an upper limit.

In a further disclosed embodiment of the apparatus, stiffener when inthe retracted position is rearward of a forward surface of a vehiclebumper beam and above a ground clearance plane of the vehicle, and inthe deployed position the stiffener is forward of the retracted positionand below the ground clearance plane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a vehicle equipped with apedestrian protection leg stiffener;

FIG. 2 is a schematic side view of the vehicle and pedestrian protectionleg stiffener of FIG. 1;

FIG. 3 is a schematic view of a linear actuator for deploying apedestrian protection leg stiffener;

FIG. 4 is a schematic side view of showing a pedestrian protection legstiffener in a deployed position;

FIGS. 5 and 6 show, in the form of a flow-chart, an example of adeployment logic for a leg stiffener system that considers vehiclesteering and braking in addition to vehicle speed; and

FIG. 7 is a system block diagram of a control system to control thestiffener position.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

Referring to FIGS. 1 and 2, a motor vehicle 10 generally comprises aleft and a right forward frame member 12, 14 oriented approximatelylongitudinally relative to the vehicle. Forward frame members 12, 14 maybe portions of a traditional ladder-type frame, of a forward vehiclesub-frame, of a unitary body/frame (“unit-body”) construction, or of anyknown motor vehicle structure. Forward frame members 12, 14 may comprisecrush cans.

A bumper assembly 16 extends generally transversely relative to thevehicle and is mounted to the left and right forward frame members 12,14 in a conventionally known manner. Bumper assembly 16 generallycomprises a rigid, high strength bumper beam 18 that is typically formedfrom steel, aluminum alloy, or a high-strength composite material. As iswell known in the art, bumper beam 18 is a structural member designed towithstand impact loads during a collision and to transfer such loads tothe forward frame member 12, 14. If the forward frame member 12, 14comprise crush cans, an impact of sufficiently high impulse will resultin the forward frame members yielding or deforming to absorb kineticenergy of the impact.

Referring to FIG. 2, Bumper assembly 16 may further comprise one or moreother components such as an upper valence 19, a lower valence 20attached to a lower portion of the bumper beam 18 and/or an air dam 22which may be formed integrally with the lower valance.

Left and right linear actuators 24, 26 are mounted adjacent to theinboard surfaces of forward frame members 12, 14, respectively. As bestseen in FIG. 2, right linear actuator 26 generally comprises a fixedportion 26 a secured to forward frame member 14 and a movable piston 26b. Right linear actuator 26 is mounted to right frame member 14 so thatpiston 26 b is linearly extendable along a deployment axis 30 that isoriented downward and forward at an angle α relative to a line Lparallel with the longitudinal axis of the vehicle. Left linear actuator24 similarly comprises a fixed portion secured to left forward framemember 12 and a movable piston extendable along a deployment axis atangle α relative to the vehicle longitudinal axis.

A lower leg stiffener 28 is mounted to the forward or distal ends of thepistons 24 b, 26 b and is moveable between a retracted position and anextended or deployed position (indicated in phantom lines in FIG. 1) byextension of the linear actuators 24, 26. Stiffener 28 may be made ofany appropriate material, such as steel, aluminum or carbon fibercomposites or plastics. For example, computer-aided engineering (CAE)simulations have been carried out in which the stiffener was modeled asa 50 mm×50 mm tube cross-section with wall thickness of 1.6 mm, formedof 6111 aluminum alloy.

As best seen in FIG. 2, when in the retracted position stiffener 28 islocated immediately below the forward frame members 12, 14 and rearwardof the forward surface of bumper beam 18. In the retracted position,stiffener 28 is preferably located above a ground clearance plane 32.Ground clearance plane 32, as is well known in the art, is an imaginaryplane normally established by drawing a straight line from a pointtangent to the front tire 34 to a lowest portion of the bumper assembly16 or any other component extending downward and/or forward from thebumper beam. Thus, ground clearance plane 32 is the inclined plane belowwhich no portion of the vehicle structure extends. The ground clearanceplane for most vehicles sold in standard-use markets usually providesfor a minimum height of running clearance and minimum degrees of rampbreak-over angle or approach angle clearance in front of the fronttires. Because stiffener 28 is located completely above the groundclearance plane 32 when retracted, it is protected from being struck byobstacles and it does not reduce the vehicle's ground clearance.

FIG. 4 shows the actuator 24 and lower leg stiffener 28 in the deployedor extended position. Actuator 26 is not visible in this side view, butis also in an extended state. In the deployed position, the linearactuators 24, 26 have been actuated to extend pistons 26 a, 26 bdownward and forward so that the stiffener 28 is below the bumper beam18 and below the ground clearance plane 32. When stiffener 28 is in thedeployed position, it prevents or inhibits a lower leg (not shown) of apedestrian from becoming trapped beneath the bumper assembly of avehicle when the vehicle strikes the pedestrian. The value of angle α atwhich deployment axes 30 are oriented relative to horizontal and thevertical position of the stiffener 28 between the ground surface and thebumper assembly 16 may be determined by the geometry of the particularmotor vehicle type and the pedestrian protection targets that the systemis in intended to meet.

FIG. 4 also shows the position of the stiffener when in the retractedposition, shown in hidden line and indicated by 28′. The retractedstiffener 28′ may be partially enclosed and/or hidden from view by thelower valance 20 or other component(s) of bumper assembly 16.Alternatively, the retracted stiffener 28′ may lie against and/or fitinto a recess in the lower structure of the bumper assembly (in valence20, for example) to present an aerodynamic shape.

Linear actuators 24, 26 may be electrically, pneumatically, orhydraulically powered. FIG. 3 is a simplified schematic diagram of onepossible embodiment employing a rotary screw-type linear actuator inwhich a reversible electric motor 40 rotates a screw 42. A nut 44engages the threads of screw 42 and is fixed relative to a piston shaft46. Accordingly, rotation of screw 42 by motor 40 results in nut 44 andthe attached piston 46 being extended or retracted depending on thedirection of motor rotation.

In recognition of data collected relating to real-worldpedestrian/vehicle collisions, pedestrian protection standards relatedto lower leg injury generally only address vehicle operation atrelatively low speeds. For example, some standards may call for avehicle to meet lower leg injury targets only in a speed range of fromapproximately 30 kph (kilometers per hour) to approximately 80 kph.Accordingly, the stiffener may be deployed only when the vehicle isoperating in this speed range. Below 30 kph the stiffener is maintainedin the retracted position where it is protected from damage. If thevehicle driver sees an obstacle that must be driven over and requiresmaximum ground clearance, he/she can slow to below 30 kph and thestiffener will be retracted. Above 80 kph, the stiffener is alsoretracted to reduce aerodynamic drag and so improve energy efficiency.

In addition, some vehicles may be operable in an Off-Road mode in whichcertain vehicle systems (suspension and/or powertrain, for example) havesettings adapted for operation on un-paved, rough surfaces and, usually,at lower speeds. Such an Off-Road mode may be selected manually by thevehicle operator (if such a switch is provided for the operator) and/ormay be triggered automatically based on certain detected parameters.When the vehicle is operating in an Off-road Mode, it is expected thatit will be traveling in an area in which pedestrians are not likely tobe present, and it is assumed that the vehicle will require the largestpossible ground-clearance to avoid striking obstacles. Therefore, in theOff-Road mode, deployment of the stiffener is inhibited regardless ofthe vehicle speed.

Even when the vehicle is travelling at speeds within the “stiffenerdeployed” range (and the Off-Road mode is not selected), there arecircumstances under which it may be favorable for the stiffener to be inthe retracted position.

FIGS. 5 and 6 illustrate, in flow-chart form, an example of a stiffenerdeployment logic that additionally takes into account vehicle steeringand braking conditions. At START in FIG. 5, the stiffener is in theretracted position and an Off-Road mode (which suppresses stiffenerdeployment, as described above) is not selected. At step 100 the vehiclespeed read and is compared at step 120 with a lower limit speed, 30 kphin this example. If the speed is below this lower limit speed (step 110,NO), the logic returns to step 100 and the stiffener is maintained inthe retracted position. If the speed is equal to or over 30 kph (step110, YES), a timer is started at step 120 and the method progresses tostep 130 where the vehicle speed continues to be read (or monitored) andcompared with the lower limit speed at step 140.

If the vehicle speed check at step 140 finds the speed has dropped below30 kph (YES), the timer is stopped (step 150) and the method returns tostep 100. If the speed remains above 30 kph (step 140, NO), the methodloops through steps 130, 140 160 until the timer exceeds a predeterminedtime (10 sec in the present example), and the method progresses to step170 where the stiffener is deployed.

Vehicle speed continues to be read at step 180 and compared with anupper limit speed (80 kph in the present example) at step 190. If theupper limit is exceeded (step 190, YES), the combination of steps 190through 240 result in the stiffener being maintained in the deployedposition until the upper speed limit it exceeded for at least apredetermined length of time (1 min in this example. If the time limitis exceeded (step 240, YES), the method reached step 250 where thestiffener is retracted.

After the stiffener is retracted, vehicle speed continues to bemonitored (260) and compared with the upper limit (270). Steps 260through 320 combine to keep the stiffener retracted unless and until thevehicle speed drops below 80 kph (or other selected upper limit speed)continuously for over 1 min (or other predetermined time), step 320,YES. The method then returns to step 100 and, running the steps 10thorough 160, the stiffener is deployed after an additional 10 sec ifthe vehicle speed remains above 30 kph for the designated time period(step 160, YES).

The timer setting in the logic shown in FIG. 5 (steps 160, 240 and 320)and their respective speed thresholds prevent unwanted, frequent cyclingbetween the retracted and deployed stiffener positions that mayotherwise occur if the vehicle is frequently crossing the selected loweror upper speed limit. It should be noted that by using a longer timethreshold to retract the stiffener than is required to deploy it (1 minin step 240 versus 10 sec in step 160, in the present example), thesystem is biased towards keeping the stiffener deployed and therebyproviding protection for the pedestrian.

Returning now to FIG. 5, step 190, if (after the stiffener is deployedat step 170) the vehicle speed remains below 80 kph (step 190, NO), themethod progresses to step 400 (see FIG. 6). If the speed again dropsbelow 30 kph (step 410, YES), a time is started (step 420) and if thetimer reaches 10 sec (step 500, YES), the stiffener is retracted at step450. This timer delay, as explained above with regards to FIG. 5,prevents undesirable cycling of the stiffener if the vehicle speedvaries frequently above and below 30 kph. While this timer delay runs,however, the remaining steps shown in FIG. 6 will reach step 450 andretract the stiffener in two cases.

At steps 430, 440, the steering angle is read (measured) and comparedwith a limit angle (60° in the present example). If the steering angleequals or exceeds the limit angle, indicating a sharp turn, thestiffener is retracted to avoid possible damage.

At step 460, the vehicle's brake system status and longitudinalacceleration are read (monitored). If the vehicle brake is applied ANDthe longitudinal vehicle acceleration exceeds a limit acceleration (0.2gin the present example), indicating an abrupt braking maneuver, thestiffener is retracted to avoid possible damage.

Taken as a whole, the logic disclosed in FIGS. 5 and 6 is effective todeploy the stiffener when it is likely to be effective in reducing thelikelihood and/or severity of pedestrian injuries, but retract thestiffener when it is unlikely to be effective and may unnecessarilyreduce ground clearance. Further, this is accomplished without excessivecycling of the deployment mechanism

FIG. 7 shows, in schematic block diagram form, an example of anapparatus capable of controlling the stiffener position in accordancewith the logic described above in relation to FIGS. 5 and 6. In thisexample, numerous vehicle performance and control inputs arecommunicated to a pedestrian safety controller 62 via, for example, anelectronic data bus such as a communication area network or CAN bus 65.The pedestrian safety controller 62 is preferably a microprocessor-baseddevice that receives necessary inputs and applies appropriate programmedlogic to direct the position of a pedestrian leg stiffener bycontrolling actuators such as, for example, the linear actuators 24, 26discussed in relation to FIGS. 1-4.

Among the inputs received by pedestrian safety controller 62 are: speeddata from a vehicle speed sensor 60; steering angle data from thevehicle steering system 74; brake activation data from a vehicle brakingsystem 70; vehicle acceleration data from an accelerometer 76 (such asan inertial measurement unit (IMU), for example); and elapsed timeinformation from a timer 78. Brake activation data from vehicle brakingsystem 70 may be a binary “brake activated/not activated” signal from anelectrical switch, or it may indicate a degree of braking applied.

An On/Off-Road Selector Switch 64 may be used to allow the driver toinhibit stiffener deployment, as described above. Other vehicle systemssuch as stability control module 66, powertrain 68, braking system 70,and adjustable suspension system 72 may also be adjusted in accordancewith the On/Off-Road Selector Switch position and/or additional inputs,as is well known in the art.

The stiffener control method(s) and system block diagram disclosed inrelation to FIGS. 5-7 are not limited to the stiffener actuationapparatus of FIGS. 1-4, but rather may be applied to any deployablepedestrian protection leg stiffener apparatus.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. A method for controlling operation of apedestrian protection stiffener of a motor vehicle comprising:retracting the stiffener from a deployed position if a vehicle brake isapplied and a longitudinal acceleration of the vehicle simultaneouslyexceeds a limit acceleration.
 2. The method of claim 1 furthercomprising: retracting the stiffener from the deployed position if ameasured speed of the vehicle drops below a lower limit.
 3. The methodof claim 2 wherein the stiffener is retracted only if the measured speedof the vehicle drops below the lower limit for longer than apredetermined length of time.
 4. The method of claim 1 furthercomprising: before the retracting step, moving the stiffener to thedeployed position when a measured speed of the vehicle rises above anupper limit.
 5. The method of claim 1 wherein the stiffener has aretracted position rearward of a forward surface of a vehicle bumperbeam and above a ground clearance plane of the vehicle, and in thedeployed position the stiffener is forward of the retracted position andbelow the ground clearance plane.
 6. A method for controlling apedestrian protection stiffener of a motor vehicle comprising: deployingthe stiffener if a vehicle speed exceeds a first value; retracting thestiffener if the vehicle speed drops below a second value; andretracting the stiffener if a vehicle brake is applied and alongitudinal vehicle acceleration simultaneously exceeds a limitacceleration.
 7. The method of claim 6 wherein the first value is equalto the second value.
 8. The method of claim 6 further comprising:retracting the stiffener if the vehicle speed rises above a third valuegreater than the first value.
 9. Apparatus comprising: a pedestrian legstiffener movably mounted to a motor vehicle; an actuator moving thestiffener between a retracted position and a deployed position; and acontroller receiving an input from a braking system of the vehicle andan input from an accelerometer and directing the actuator to positionthe stiffener in the retracted position if the braking system inputindicates a vehicle brake is applied and the accelerometer inputsimultaneously indicates that the vehicle is experiencing a longitudinalacceleration above a limit acceleration.
 10. The apparatus of claim 9wherein: the controller further receives an input from a vehicle speedsensor and directs the actuator to position the stiffener in theretracted position if the speed sensor input indicates that a vehiclespeed is below a lower limit.
 11. The apparatus of claim 10 wherein thecontroller directs the actuator to position the stiffener in theretracted position only if the vehicle speed is below the lower limitfor longer than a predetermined length of time.
 12. The apparatus ofclaim 9 wherein: the controller further receives an input from a vehiclespeed sensor and directs the actuator to position the stiffener in thedeployed position if the speed sensor input indicates that a vehiclespeed exceeds an upper limit.
 13. The apparatus of claim 9 wherein thestiffener in the retracted position is rearward of a forward surface ofa vehicle bumper beam and above a ground clearance plane of the vehicle,and in the deployed position the stiffener is forward of the retractedposition and below the ground clearance plane.